Indicators, Acids, and Alkalis

Question 1

What is an indicator?

Answer 1

An indicator is just something that changes colour depending on whether it’s in an acid or in an alkali.

Question 2

What is litmus paper?

Answer 2

Litmus paper is quite a popular indicator, but it only tells us whether a liquid is an acid or an alkali - it does not say how strong it is. Acids turn litmus paper red and alkalis turn it blue.

Question 3

What is universal indicator?

Answer 3

Universal indicator solution is a very useful mixture of dyes which gives the colours shown in a pH chart.

Question 4

How can you make red cabbage indicator?

Answer 4

1) Stir some cut leaves of red cabbage in a beaker of boiling water to obtain a red solution.
2) Filter the solution to remove all salts.
3) Add to acid or alkali.
It will turn pink/red if it is an acid, and it will turn green/yellow if it is an alkali.

Question 5

What does the pH scale show?

Answer 5

The pH scale shows the strength of acids and alkalis. The pH scale goes from 0 to 14. pH can also be shown by colour universal indicator turns.

Question 6

What is the pH of an acid?

Answer 6

Anything with a pH below 7 is an acid and will turn universal indicator red, orange or yellow.

Question 7

What is the pH of the strongest acids?

Answer 7

The strongest acids have a pH of 0.

Question 8

What is the pH of an alkali?

Answer 8

Anything with a pH above 7 is an alkali and will turn universal indicator blue or purple.

Question 9

What is the pH of the strongest alkalis?

Answer 9

The strongest alkalis have a pH of 14.

Question 10

What is the pH of a neutral substance?

Answer 10

A neutral substance (e.g. pure water) has a pH of 7 and will turn universal indicator green.

Question 11

What do acids and alkalis do to each other?

Answer 11

Acids and Alkalis neutralise each other.

Question 12

What is formed when acids react with alkalis?

Answer 12

Acids react with alkalis to form a neutral solution of a salt and water.

Question 13

What is the word equation for neutralisation?

Answer 13

acid + alkali ==> salt + water

Question 14

Why is it known as a neutralisation reaction?

Answer 14

This is known as a neutralisation reaction because the products have a neutral pH (a pH of 7).

Question 15

What are everyday uses of neutralisation?

Answer 15

Treating indigestion or using toothpaste

Question 16

What is the test and result for carbon dioxide?

Answer 16

Test: Bubble the gas through limewater
Result: Limewater turns milky/cloudy

Question 17

What is the test and result for hydrogen?

Answer 17

Test: Place a lighted splint in a test tube containing the gas
Result: There will be a squeaky pop

Question 18

What is the test and result for water?

Answer 18

Test: Transfer liquid into a sample of anhydrous copper (II) sulfate
Result: Anhydrous copper (II) sulfate turns blue

Question 19

What is the test and result for oxygen?

Answer 19

Test: Place a glowing splint in a test tube containing the gas
Result: Glowing splint relights

Question 20

What do most fossil fuels contain?

Answer 20

Most fossil fuels contain sulfur in compounds present as impurities.

Question 21

What happens when fossil fuels are burnt?

Answer 21

When we burn the fuel, the sulfur is oxidised. It turns into sulfur dioxide (SO2) gas.

Question 22

What do power stations give off?

Answer 22

Power stations burning coal or oil give off most sulfur dioxide; this is the main cause of acid rain.

Question 23

What happens with sulfur dioxide?

Answer 23

It dissolves in rainwater and reacts with oxygen in the air, to form sulfuric acid.

Question 24

What are some effects of acid rain?

Answer 24

• Trees are damaged and even killed
• Lakes in Norway and Sweden now have no fish in them
• Buildings and metal structures are attacked